To improve driving dynamics in motor vehicles, powertrains are used which can be adapted to the driving conditions applicable at the time. For example in hybrid vehicles, in certain driving situations it may be advantageous to separate an electric motor of the hybrid drive from the other components of the powertrain, such as when the internal combustion engine of the hybrid drive is supplying the required drive torque and the drive power of the electric motor is not required.
Here clutches are used which serve to selectively couple together the components of the powertrain or separate these from each other. A clutch may also ensure a safety shut-off in the event of operating faults.
In the case of a hybrid vehicle, the vehicle may be kept in motion by an internal combustion engine, wherein the drive movement of the vehicle axle driven by the internal combustion engine is transmitted to the wheels of the second vehicle axle via a gear mechanism, which is also rotating in this situation. Due to losses and friction which occur throughout the entire arrangement of the powertrain, an electromotive drive assembly is also accelerated and hence dragged passively. This behavior normally contributes substantially to shortening the synchronization time of a clutch.
Such a powertrain is known from DE 10 2000 055 249 A1. This discloses both a device and a method for operating a claw clutch in a motor vehicle with an electromotive drive, wherein the two clutch parts of the claw clutch transmit a force between the electromotive drive and an axle supporting the wheels of the motor vehicle, and before closure of the claw clutch are set to a predefined rotation speed difference between the axle and the electromotive drive, wherein the predefined rotation speed difference is formed from a synchronization rotation speed of the electromotive drive and a rotation speed of the motor vehicle wheels.
The term “predefined rotation speed difference” here refers to the last phase of a previously initiated clutch engagement process. The clutch element which is connected to the vehicle axle has a rotation speed which is higher or lower by a differential rotation speed than the synchronization rotation speed, which ensures that the two clutch elements of the claw clutch can intermesh in that a tooth of one clutch element engages in a gap of the other clutch element.
The device also disclosed in DE 10 2009 055 249 A1 is characterized in that means are present which accelerate the passive electromotive drive during drive operation of the motor vehicle with the claw clutch open. Advantageously, the electromotive drive is operated in an idling operating mode and is accelerated by a drag moment of a gear mechanism, wherein the gear mechanism is moved via the axle carrying the wheels of the moving motor vehicle. The drag moment is amplified if the electromotive drive and the claw clutch are arranged in the transmission oil of the attached gear mechanism.
Because of the spatial conditions in certain vehicles and to improve the kinematics, a substantially different arrangement of the components of the powertrain from that given in DE 10 2009 055 249 A1 may be advantageous.
In particular, a coaxial arrangement of a differential gear, an electromotive drive assembly and a clutch on a vehicle axle allows a particularly compact, lightweight and space-saving configuration of a powertrain for a motor vehicle.
It is therefore the object of the invention to improve a method for operating a powertrain in relation to the known embodiments.